Wireless power transfer systems typically include primary side transmitters and secondary side receivers and are employed to transfer power wirelessly over an isolation barrier to facilitate a convenient mode for powering or charging batteries of mobile devices. Mobile devices can include cell phones, tablet PCs, digital cameras, medical electronic implants, industrial equipment, or medical equipment where having direct electrical contacts to supply power to the device is not desirable.
The most common system for wireless power transmission is via induction methods wherein a transformer is employed to transfer power from a primary side winding to a secondary side winding over an isolation barrier in the transformer. Thus, in a battery charging application, a charging pad may be employed to allow a mobile device such as a cell phone to receive its charge when placed near the charging pad. The mobile device can be connected to the secondary winding and receive its power wirelessly from the primary winding which can in turn be powered from a wall outlet for example. This allows the mobile device to be charged without being directly plugged into a power source which offers great convenience to the user.
Unfortunately, power sources that power the primary side of the wireless power system are highly variable and offer variable amounts of power. For example, a wall adapter may be able to deliver substantially more power that a universal serial bus (USB) adapter. Current wireless power transfer systems will shut down if a minimum amount of input power is not available to the system. Shut down conditions provide no charging solution for the respective user. Other wireless power transfer systems (e.g., light energy transfer systems) may also suffer from similar sourcing problems.